The Electronic Structure of the FeSe / Ti1+xO2 / SrTiO3 Interface

FeSe / Ti1 xO2 / SrTiO3 界面的电子结构

• 批准号: 2032810
• 负责人: Hunter Sims
• 金额: $ 10.19万
• 依托单位: Francis Marion University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-02-01 至 2023-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2032810&HistoricalAwards=false
• 关键词: Electronic; Structure; FeSe; Ti1+xO2; SrTiO3

The promise of transmitting electricity without loss makes superconductivity at standard temperature and pressure one of the most tantalizing goals in materials science. However, a comprehensive explanation of high-temperature superconductivity remains elusive. To chart a path forward, scientists must study individual materials to try to understand how they work and what they have in common. This project will provide computational tools for the study of how superconducting materials react to changes in their atomic structure. Understanding these changes allows researchers to predict ways to increase the operating temperature of a superconducting material, allowing experiments to focus on the most promising candidates. These tools will be applied to the case of iron selenide (FeSe) deposited on strontium titanate (SrTiO3). A single three-atom-thick layer of FeSe grown on SrTiO3 remains superconducting up to temperatures almost 10 times greater than larger crystals of pure FeSe. The methods implemented in this project will clarify the properties of this material and may suggest how to design new superconductors. The project will also allow students from a small undergraduate university to accompany the principal investigator to a national laboratory where they will gain computational research skills and further develop their identity as scientists. Technical DescriptionMonolayer FeSe on SrTiO3 has been actively studied since the discovery of its enhanced superconducting temperature Tc of 60 – 80 K, compared to around 8 K in bulk FeSe. Theoretical investigations have focused on a pure FeSe / SrTiO3 interface, but atomic-resolution scanning transmission electron microscope (STEM) images have revealed the existence of an additional titanium-oxide layer between the SrTiO3 substrate and FeSe. The P.I. recently published computational results that demonstrate that this layer exhibits a titanium excess that can participate in electron-doping the FeSe monolayer. This doping is thought to be important in increasing Tc in this system. While these density functional theory results provide a good description of the atomic structure of this material, there are technical and fundamental limits to such methods’ ability to accurately describe a realistic heterostructure. After extracting material-specific model parameters from these calculations, the P.I. will perform more sophisticated calculations that will clarify which of the properties of the system are most important to the superconducting state. The effect of disorder or different ordering in the extra interfacial layer will be explored by constructing multiple structural configurations and averaging over their band structures. Further, surface Green functions will be computed to determine the electronic structure of the monolayer and interfacial layer on a more realistic semi-infinite substrate. Such results can also provide insight into how similar increases in Tc might be engineered in other materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在不损失的情况下传输电力的希望使在标准温度和压力下的超导性是材料科学中最诱人的目标之一。但是，对高​​温超导性的全面解释仍然难以捉摸。为了绘制前进的途径，科学家必须研究各个材料，以尝试了解它们的工作方式和共同点。该项目将提供计算工具，以研究超导材料如何应对其原子结构的变化。了解这些变化使研究人员能够预测增加超导材料的工作温度的方法，从而使实验专注于最有望的候选者。这些工具将应用于沉积在钛酸盐（SRTIO3）上的硒化铁（FESE）的情况下。在SRTIO3上生长的单个FESE的单个三厚层仍然超导至温度，其温度是纯FESE较大晶体的近10倍。该项目中实施的方法将阐明该材料的属性，并可能建议如何设计新的超导体。该项目还将允许一所小型大学的学生参与首席研究员到国家实验室，在那里他们将获得计算研究技能，并进一步发展他们作为科学家的身份。自从发现其增强的超导温度TC为60 - 80 K以来，SRTIO3上的技术描述Monolayer FESE已被积极研究，而散装FESE则约为8 K。理论研究集中在纯FESE / SRTIO3界面上，但是原子分辨率扫描透射电子显微镜（STEM）图像揭示了SRTIO3底物和FESE之间存在额外的钛氧化物层。 P.I.最近发表的计算结果表明，该层表现出超过钛，可以参与电子掺杂FESE单层。人们认为这种掺杂在增加该系统中的TC中很重要。尽管这些密度功能理论的结果很好地描述了该材料的原子结构，但这种方法可以准确描述现实的异质结构的技术和基本限制。从这些计算中提取特定于材料的模型参数后，P.I。将执行更复杂的计算，以阐明系统的哪些特性对于超导状态最重要。通过构建多种结构构型和在其带状结构上平均，将探索杂物或不同界面中不同顺序的效果。此外，将计算表面绿色函数，以确定单层和界面层的电子结构在更逼真的半无限基板上。这种结果还可以洞悉其他材料中如何设计TC的类似增长。该奖项反映了NSF的法定任务，并通过使用基金会的知识分子优点和更广泛的影响标准来评估，被视为珍贵的支持。